The present invention relates generally to portable battery operated electronic equipment, and more particularly to a battery compartment for use with such equipment in which electrical connection to the battery is prevented in the event one or more of the cells thereof is incorrectly oriented within the compartment. The compartment is particularly well suited for use in battery operated medical electronic equipment such as, for example, a cardiac pacer system analyzer.
Safety in the use of electrically operated equipment during treatment of a medical disorder requires that adequate measures be taken to prevent inadvertent patient exposure to potentially endangering electrical currents. While efforts directed to preventing such contact have proven effective, patient safety can be further enhanced by removing all high voltage sources from the vicinity of the patient. The use of low voltage electrochemical cells to power medical electronic equipment is therefore attractive since step-down power supplies, and the relatively high voltage alternating current required for their operation, can be entirely eliminated.
While battery operation is attractive from the viewpoints of safety and portability, these benefits are not derived without some cost. In particular, the need for periodic user-replacement of the battery enhances the probability that one or more of the battery cells will be incorrectly polarized within the battery compartment, resulting in incorrect battery voltage or polarity, a general deterioration of equipment performance, and possible damage to equipment circuitry. It is therefore desirable to reduce or eliminate the possibility of such inadvertent misorientation of cells within a battery compartment. Accordingly, electronic as well as mechanical techniques have been employed to avoid the adverse consequences of incorrect cell orientation.
One well known electronic technique is the provision of semiconductor diodes in the battery circuit to prevent the application of reverse voltages to polarity sensitive circuit components. While this technique is effective in preventing circuit damage in the event of incorrect battery polarity, it is ineffective when only one or two cells of a multi-cell battery are misoriented since, in such a case, the resulting battery voltage will not be of opposite polarity, but will merely be of lower amplitude. Furthermore, the voltage drop across one or more forward biased diodes during normal operation may significantly reduce available battery voltage.
Mechanical techniques have generally been utilized in conjunction with battery types in which the battery terminals are either asymmetrically located on the battery casing or are of differing size or shape. Preferably the differences between the positive and negative polarity battery terminals are such that respective battery compartment contacts can only engage one or the other of such terminals. This technique has typically been employed in conjunction with relatively more expensive single-unit, multi-cell, batteries rather than with the more inexpensive cylindrical "D" or "C" electrochemical cells having terminals on opposite ends.
The present invention is directed to a battery compartment for receiving one or more cylindrical electrochemical cells of the type having terminals at opposite ends. The battery compartment includes terminals constructed so as to establish electrical contact with one or the other, but not both, of the terminal types utilized in such cells. In a battery compartment constructed in accordance with the invention, electrical continuity between the battery and the device circuitry will be established only if each of the cells is correctly oriented within the battery compartment.
In view of the foregoing it is a general object of the present invention to provide a new and improved battery compartment for battery operated electronic apparatus.
It is a more specific object of the present invention to provide a battery compartment which guards against inadvertent misorientation of battery cells within.
It is a still more specific object of the present invention to provide an improved battery compartment in which the battery is automatically disconnected from the apparatus circuitry in the event one or more cells are misoriented within the compartment.